Capacitors are used in implantable defibrillators for accumulating an electrical charge from internal batteries, so that rapid discharge of the capacitor may provide a substantial shock for cardiac therapy. A single capacitor has a basic decay pattern in which the voltage begins at a nearly instantaneous spike, and decays at a rate determined by the characteristics of the device. When different discharge characteristics are desired, such as when an extended initial period of higher voltage is needed, a second capacitor has been used. This permits simultaneous discharge to provide a maximum voltage or current, with connection in series or parallel. The time of discharge of the different capacitors may be staggered to provide a two-peak output, with the second discharge occurring before the voltage level from the first has dropped below a selected threshold.
To provide additional flexibility and controllability of the output wave form, more individual capacitors may be used. However, multiple separate capacitors are less volume efficient than a single larger capacitor, in that they have a lesser aggregate capacitance per unit volume. This is a particular concern in implantable medical devices and numerous other applications in which miniaturization is important. Thus, there is a trade off between the output control and size.
The present invention overcomes the limitations of the prior art by providing an electrolytic capacitor having several cathode layers and several anode layers stacked in a single housing. At least some of the anode layers are electrically interconnected in a group electrically isolated from another group of electrically interconnected anodes. Separate electrical connections permit the separate groups to be independently connected to external circuitry.